The United States and Britain say they’re considering new economic sanctions on the Syrian and Russian governments because of their conduct in war-ravaged Aleppo.

After a 10-nation meeting in London, US Secretary of State John Kerry said on Sunday crimes against humanity were occurring daily in Syria.

Kerry and British Foreign Secretary Boris Johnson are expressing hope about a diplomatic effort with Russia and several other countries that Kerry began on Saturday.

But they said they’re planning to increase pressure on Russia and Syria to halt air strikes on Aleppo, Syria’s largest city.

Johnson and Kerry said sanctions could be applied against Syria and its supporters.

Johnson also spoke of trying to advance prosecutions of “war criminals”.

John Kerry described what was happening in Aleppo as a “horrendous step back in time to a kind of barbarism”, and the largest humanitarian disaster since World War II.

He sounded frustrated as reporters pushed him on what actual action the world planned to take in Syria.

“We are pursuing diplomacy because that is the only option we have. I hear a lot of people saying ‘where’s the action’, but WHAT is the action?”

Over 500,000 deaths in Syria and a bottomless pit of diplomacy. Here is Kerry's solution. https://t.co/eMf9JWRG7L

— Benjamin Weinthal (@BenWeinthal) October 16, 2016